#include <bits/stdc++.h>
using namespace std;
long long n, m;
string word, path, iznos[2000][2000];
char unos[2000][2000];
int main (){
ios::sync_with_stdio(0);
cin.tie(0);
cin >> n >> m;
for (int i=0;i<n;i++){
cin >> word;
for(int j=0;j<m;j++){
unos[i][j] = word[j];
}
}
path = unos[0][0];
int i=0, j=0;
while (i!=n-1 and j!=m-1){
if (unos[i][j+1] > unos[i+1][j]){
i++;
path = path + unos[i][j];
}
else if (unos[i][j+1] > unos[i+1][j]){
j++;
path = path + unos[i][j];
}
}
while (i!=n-1){
i++;
path = path + unos[i][j];
}
while (j!=m-1){
j++;
path = path + unos[i][j];
}
cout << path;
return 0;
}
